Introduction
Time, Speed and Distance (TSD) is one of the highest-yield chapters in every Bangladeshi government-job exam — BCS Preliminary, Bank (Combined/AUST/BB), and IT-officer written papers. A single, tiny relationship governs the entire topic, yet examiners spin dozens of question types from it: simple travel problems, average speed, relative speed, trains crossing poles and platforms, boats in streams, and races. If you master the one core formula and the handful of standard "twists", you can solve almost every TSD problem in under a minute — often mentally.
This lesson builds the topic from first principles, defines every term, gives the intuition behind each formula, and then drills the standard exam patterns with fully worked solutions.
Learning Objectives
By the end of this lesson you will be able to:
- State and manipulate the fundamental relation Distance = Speed × Time in all three forms.
- Convert fluently between km/h and m/s and other units.
- Correctly compute average speed (and know why it is not the arithmetic mean of speeds).
- Apply direct and inverse proportionality to solve "if speed changes" problems.
- Use relative speed for same-direction and opposite-direction motion, and for overtaking/meeting problems.
- Solve all train problems: crossing a pole, a platform, another train, or a moving object.
- Solve boats-and-streams problems using upstream/downstream logic.
- Solve basic races and circular-track problems.
- Avoid the classic traps examiners set in this chapter.